1. Field of the Invention
The invention relates to a device for aligning sheets of a sheet stack against two sheet abutments which are disposed perpendicularly to each other, said device comprising at least one aligning element which is arranged about an axis inclined with respect to the surface of the sheet stack and includes a friction element.
2. Description of the Prior Art
A device for aligning sheet-type articles is disclosed in U.S. Pat. No. 3,970,299 (issued Jul. 20, 1976, in the names of Emil J. Berger, Jr. and John M. Mitchard). In that device, sheet-type articles are transported on a conveying means. To facilitate uniform alignment of the sheets, guide rails are secured to the transport means and arranged both vertically to, and parallely with the direction of transport. For aligning the sheets with respect to the guide rail extending in parallel with the transport direction, a rotating brush is used which exerts a force on the sheet-type articles in order to move them into engagement with the lateral guide rail. The constant contact of the brush used in the prior art device is disadvantageous since alignment in the two spatial directions cannot be carried out separately. Moreover, the known device serves for aligning individual sheets transported along a travel path rather than sheets arriving on a sheet stack.
Japanese Patent Application 59-120746 discloses a paper aligning device for a copier, in which the sheet is aligned with a guide provided laterally in the direction of transport of the sheet. At the beginning of the aligning operation, the aligning mechanism is arranged at an angle to the direction of transport and thus applies a motion component to the sheet in a direction transversely perpendicular to the direction of transport. As soon as the sheet has been aligned transversely perpendicular to the direction of transport, the aligning mechanism is urged into a position parallel with the direction of transport whereupon the sheet is completely aligned parallel to the transport direction. This aligning device is disadvantageous in that the continuously operating aligning mechanism obstructs free movement of successive sheets.
An International Patent Application WO 89/08599 describes a depositing mechanism for stacking sheet-type record carders in an exit tray of a printing device. Using such depositing mechanisms, record carriers are to be stacked in the exit tray such that the record carriers forming part of different printing orders are clearly identified in the deposited stack. Depending on the printing order, the record carriers are aligned against the side walls of the exit tray by rotary advancing elements. The advancing elements feature radially projecting flexible wings. The force component required for alignment is transmitted to the record carrier by frictional contact between the wings of the rotary advancing element and the record carder. The aforementioned disadvantages, e.g. the obstruction of successive sheets, are also encountered in this device. In addition, the simultaneous action of force components in two spatial directions can cause damage to the sheets.